1. Field of the Invention
The present invention relates to a paper supply apparatus which feeds roll paper wound around a winding core, and an image formation device which is equipped with this paper supply apparatus, and more particularly relates to a paper supply apparatus and image formation device provided with a sensor for detecting when there is no more roll paper.
2. Description of the Related Art
Apparatuses which are mounted at image formation devices, such as copiers, facsimile machines, printers and the like, and which supply recording paper wound in the form of a roll (hereinafter referred to as roll paper) are well known. At a roll paper paper supply apparatus, accurate detection of a paper end when there is no more roll paper and detection of the paper end without any influence from the type of the paper are difficult, and paper supply apparatuses with various detection methods have been proposed heretofore.
For example, a paper supply apparatus has been proposed in which an outer peripheral surface of a winding core around which roll paper is wound is colored black, a light-emitting member irradiates light toward the roll paper that has been installed in the paper supply apparatus, and a reflection-type sensor which measures an amount of light reflected from the roll paper is provided. A paper end is detected in accordance with a difference between an amount of light reflected when there is roll paper and an amount of light reflected from the outer peripheral face of the winding core when there is no more roll paper.
However, with the method described above, it is necessary that winding cores be colored black. Moreover, even given the same black color, errors may occur in paper end detection because of some winding cores featuring glossiness and others not, and there are many limitations on materials and fabrication methods of the winding cores. Furthermore, there is also a problem in that errors may occur in paper end detection in cases in which the paper has high transparency.
For another method, for example, a detection apparatus 200 of Japanese Patent Application Laid-Open (JP-A) No. 05-338335, as shown in FIG. 10, has been proposed. At this detection apparatus 200, a slit plate 204 is attached to a roll paper fixing shaft 202, which rotates in accordance with an operation of drawing of roll paper P (paper supply and conveyance). A photosensor 206 is provided, which detects slits 204A formed in the slit plate 204. Hence, the slits 204A of the slit plate 204 which rotates in accordance with conveyance of the roll paper P are detected by the photosensor 206, and a remaining amount of roll paper is detected on the basis of a period of signals that the photosensor 206 outputs. Further, for this method, it has been written that the fact that there is no more roll paper can be detected by the slit plate 204 consequently not rotating any more and the above-mentioned signals not being generated.
Thus, when the detection apparatus 200 as described in JP-A No. 05-338335 is employed, it is possible to detect changes in an outer diameter of the roll paper P, and it is possible to detect that there is no more roll paper P from the fact that the roll paper fixing shaft 202 is not rotating any more.
However, with ordinary roll papers, a trailing end portion is often fixed to the winding core. In such a case, when there is no more roll paper, it is not possible to draw out the roll paper further. Therefore, the roll paper slips at a conveyance roller section. At this time, if the slit plate 204 is fixed to the roll paper fixing shaft 202, as in the method described in JP-A No. 05-338335, the slit plate 204 does not rotate, but small agitations thereof occur repeatedly. As a result, it is mistakenly detected that pulses corresponding to rotation of the roll paper are being generated. In consequence, a failure in which the detection of there being no more roll paper is greatly delayed occurs and, depending on circumstances, a failure in which a paper jam is mistakenly detected occurs.
To avoid erroneous detection of small oscillations, a method in which a spacing of the slits of the slit plate is widened has been considered. However, in such a case, a problem of it not being possible to precisely detect a remaining amount of the roll paper would occur.